1. Field of the Invention
The present invention relates to a pressure transducer, and more particularly to a differential-pressure transducer having two sensors cross-coupled and independently excited.
2. General Background and State of the Art
Differential pressure sensors are used to measure pressure differences between two pressure sources. It is known to use separate Wheatstone Bridge arrangements of interconnected resistances as the pressure sensors for measuring each of the two pressure sources. Ideally, in order to provide an accurate differential pressure measurement, the output voltage versus pressure characteristics for each of the bridge pressure sensors should be similar and should remain similar despite factors such as changing temperature and acceleration. U.S. Pat. No. 6,023,978 to Dauenhauer et al. electrically cross-couples the bridge pressure sensors to compensate for temperature and acceleration induced errors. However, Dauenhauer suffers from the disadvantage of requiring that the two sensors have substantially similar or substantially identical error characteristics in order for the cross-coupling to compensate for errors. In practice it is difficult to find sensors with such closely matching error characteristics. This results in reduced accuracy when using a design such as described by Dauenhauer. It would be desirable to provide compensation for the sensors so that they do not need to have substantially similar or substantially identical error characteristics for use as differential pressure sensors.
One important application for differential pressure sensors is in the automobile industry, where they are used to measure the pressure difference between an engine""s exhaust and intake manifolds. In such applications, the sensors are exposed to harsh contaminants. It is desirable to isolate the sensor from the surrounding contaminants while still accurately measuring pressure. U.S. Pat. No. 6,023,978 to Dauenhauer does provide isolation for the pressure sensors used in a differential pressure sensor layout, but in a rather bulky package. It would be desirable to isolate the sensors from harsh contaminants by enclosing them in a compact package.
A general object of the present invention is to provide a differential pressure transducer that will provide accurate differential pressure measurements over a range of pressures and temperatures. Another objective is to protect the electronics from contaminants while packaging the transducer within a compact housing. These goals are achieved by the present invention comprising a first pressure sensor having a first sensitivity and excited by a first voltage, a second pressure sensor having a second sensitivity different from the first sensitivity and excited by a second voltage different from the first voltage, and wherein the first and second voltages are independently adjustable to increase or decrease the sensitivities of the first and second sensors to substantially match each other, and wherein the outputs of the sensors are cross-coupled to each other to reduce the offset difference errors between the pressure sensors.
These goals are also achieved by a method for matching the output characteristics of a first and a second pressure sensor comprising the steps of, applying a first excitation to the first pressure sensor, applying a second excitation different than said first excitation to the second pressure sensor, independently adjusting the first and second excitations to increase or decrease the sensitivities of the first and second sensors to substantially match each other, and cross-coupling the outputs of the sensors to reduce the offset difference errors between the pressure sensors.